Question

in this experiment, spectrophotometric absorbance values were used to represent the concentration of the complex ion. what characteristic of the complex ion allows it to be studied by spectrophotometry

Answer 1

Ans. The transition elements form complex ions as being the central atom in the complex. The transition of electrons from one to another energy level varies depending on the type of central atom, type and number of molecules or ions (i.e. ligands) linked to the central atom and net charge on the complex ion.

So, the color of a complex ion, and in turn, its absorption maxima is almost unique to its identity.

For example-

            I. [Co(H₂O)₆]³⁺ has absorption maxima at 600 nm. Other complex ions with same central atom and number of ligands, but different ligands have different absorption maxima as follow-

            [Co(NH₃)₆]³⁺ has absorption maxima at 475 nm.

            [Co(CN)₆]^3- has absorption maxima at 310 nm.

            II. The absorption maxima also changes depending on the number of ligands and charge for the same central atom-

            [Co(NH₃)₆]Cl₃             , [Co(NH₃)₅Cl]Cl₂       ,[Co(NH3)₄Cl₂]Cl have their characteristic absorption maxima.

# So measuring the absorption at specified wavelength of the specified complex ion. A change in absorption for that complex indicates change in its concentration. Spectroscopy can be used to measure the increase or decrease in the concentration of the specified complex during a chemical reaction.

Therefore, characteristic absorption maxima of each complex ion enables their behavior (type of reaction, oxidation states, types and number of ligands, etc.) during a chemical reaction